Gasohol has been suggested widely as a substitute for gasoline and for combustion in internal-combustion engines. Typically, gasohol comprises a mixture of anhydrous alcohol and gasoline, with the alcohol present in an amount sufficient to be soluble in the gasoline. More particularly, gasohol is typically a mixture of approximately 6% to 12% by weight of alcohol, typically methanol or ethanol, and gasoline. The gasohol may contain other suitable additives, such as leaded or other antiknock additives, and, where applicable, surfactants, detergents, octane enhancers and promoters, such as tertiary methylbutyl ethyl ether and other additives, employed to enhance the combustion and performance of gasoline.
In the production of gasohol, substantially anhydrous alcohol is required for admixture with the gasoline, because of the very low water tolerance of the resulting gasohol mixture. This water tolerance often is in the range of approximately 0.2 to 0.5 weight percent of water. Higher amounts of water typically provide for unstable gasohol mixtures and lead to complete or partial separation of the water from the gasoline, the water being soluble in the methanol or ethanol, but insoluble in the gasoline, whether the gasoline is composed of highly aromatic or aliphatic components or a combination thereof.
Alcohols suitable for use in gasohol, particularly methanol and ethanol, are commonly made by the fermentation of various materials, such as sugar, corn and other grain-like or natural, fermentable materials. Fermentation broths or solutions produced often will contain up to approximately 12% alcohol in water; for example, 3% to 10%. The alcohol is separated from the water in the fermentation broth usually by a distillation process, which consumes a large amount of thermal energy. The production of anhydrous ethanol in particular requires an additional distillation step often utilizing an entraining or dehydrating solvent, such as benzene or other suitable liquid, to form a ternary solution. The addition of the benzene or other liquid is required, since ethanol and water form an azeotrope of approximately 95% alcohol and 5% water. The addition of benzene is required to permit the preparation of an anhydrous ethanol.
It would be most desirable to provide for the direct preparation of a gasohol from a fermentation broth and without the use of large amounts of thermal energy, as required in distillation, or the formation of azeotropes, with the need to add dehydrating solvents.